1. Field of the Invention
This invention relates to an antiglare film which is preferably applied on a surface of a twisted nematic (TN) type or vertical alignment (VA) type of transmission liquid crystal display (LCD).
2. Description of the Related Art
In the field of displays such as LCD, CRT (Cathode Ray Tube) display, ELD (Electroluminescence Display), and PDP (Plasma Display), providing on the display surface an antiglare film having a concave-convex structure on the surface is known as a means for preventing the degradation of visibility caused by reflection of external light on the display surface during viewing.
The following methods are known for producing such antiglare films:                a method of forming a concave-convex structure on an antiglare film surface by emboss processing;        a method of coating a coating liquid obtained by admixing particles to a binder matrix forming material and dispersing the particles in the binder matrix, thereby forming a concave-convex structure on an antiglare film surface.        
In an antiglare film having on the surface thereof a concave-convex structure formed by the above-described methods, the external light falling on the antiglare film is scattered by the concave-convex structure of the surface. As a result, the image of external light becomes smudgy and the degradation of visibility caused by the reflection of external light on the display surface can be prevented.
In the antiglare film in which convexities and concavities have been formed on the surface by emboss processing, surface convexities and concavities can be completely controlled. As a result, reproducibility is good. However, the problem is that where defects or foreign matter are present on the emboss roll, the defects spaced by a roll pitch appear on the film.
On the other hand, an antiglare film using a binder matrix and particles can be produced by using fewer operations than the antiglare film employing the emboss processing. As a result, the antiglare film can be manufactured at a low cost. Accordingly, antiglare films of a variety of forms in which particles are dispersed in a binder matrix are known (Japanese Patent Application Publication (JP-A-6-18706) No. 6-18706).
Various techniques have been disclosed with respect to an antiglare film using a binder matrix and particles. For example, the following methods for producing antiglare films using a binder matrix and particles have been disclosed:                a method using a binder matrix resin, spherical particles, and particles of irregular shape (JP-A-2003-260748);        a method using a binder matrix resin and particles of a plurality of different diameters (JP-A-2004-004777);        a method of using a film having surface convexities and concavities in which the cross-sectional area of convexities is specified (JP-A-2003-004903).        
The following methods have also been disclosed:                a method of using internal scattering in combination with external scattering and setting an internal haze of an antiglare film to 1-15% and a surface haze to 7-30% (JP-A-11-305010);        a method of using a binder resin and particles with a size of 0.5-5 μm and setting the difference in refractive index between the resin and the particles to 0.02-0.2 (JP-A-11-326608);        a method of using a binder resin and particles with a size of 1-5 μm and setting the difference in refractive index between the resin and the particles to 0.05-0.15, and a method in which the properties of the solvent used and the surface roughness are set within the predetermined ranges (JP-A-2000-338310);        a method of using a binder resin and a plurality of particles and setting the difference in refractive index between the resin and the particles to 0.03-0.2 (JP-A-2000-180611);        a method of setting a surface haze to 3 or more and setting the difference between a haze value in the normal direction and a haze value in the direction at ±60° to 4 or less with the object of reducing the variations in hue and the decrease in contrast occurring when the viewing angle changes (JP-A-11-160505).        
Thus, antiglare films of various configurations created to attain a variety of purposes have been disclosed.
The properties of antiglare films used for the front surface of displays vary depending on the type and application etc. of the display. In other words, the optimum antiglare film depends on the display category, resolution or purpose of use. Therefore, a large number of different types of antiglare films are required according to the application of the display.
Among various display devices, a TN type LCD and VA type LCD often have a problem of an occurrence of a color change and/or a gray scale inversion of an image presented on a display depending on the arrangement of the display device and observer's location. In other words, an observer receives a different colored image when being in front of the display from an image which is received when being at a point in an oblique direction.
It is an object of the present invention to provide an antiglare film having not only an antiglare function of preventing external light from falling on the display surface when applied on a surface of a TN type LCD or a VA type LCD but also a color compensation function of preventing a gray scale inversion and a color change which can be perceived from a point in an oblique direction.